1. Field of the Invention
This invention relates to the field of packaging systems for automated component handling. Specifically, the present invention relates to carrier tape packaging systems utilizing pressure sensitive adhesive (PSA) tape for component retention. More particularly, the present invention incorporates calibrated levels of low tack adhesion within compartments of adhesive backed carrier tapes.
2. Description of the Prior Art
Three basic forms of carrier tape as defined by Industry Standards are presently utilized for packing a wide range of electronic components of varied shapes and sizes in tape and reel formats to facilitate automated processing and assembly handing of these devices. These basic forms of carrier tape are broadly defined by current Industry Standards as: Embossed; Punched; and Adhesive Backed.
Embossed Carrier Tape: (also known as pocket tape or blister tape) consists of a plurality of tub-like cavities formed in continuous lengths of plastic to fit the “3D” outline dimensions of each specific size and shape of device to be placed therein, then sealed for retention in the cavities by a top cover tape of continuous length.Punched Carrier Tape: Comprises a plurality of rectangular-shaped holes pierced through continuous lengths of carrier material (typically paper). Holes are sized to fit the X-Y dimensions of devices to be placed therein and comprise cavities to retain components therein by dual cover tapes of continuous length, sealed to both sides of the punched carrier tape cavities.Adhesive Backed Carrier Tape: Comprises a plurality of compartments of maximum practical size consistent with each industry standard carrier tape width, pierced through continuous lengths of carrier tape material (typically plastic) to which one or more strips at pressure sensitive adhesive tape are affixed to one side to provide an adhesive base within each compartment to retain components placed thereon.
None of the three aforesaid basic forms of carrier tapes offered for sale commercially provide viable solutions for high-speed automated handling of the proliferation of vanishingly small electronic components whose dimensions together with unit weight continue to diminish, seemingly without limit. The vast market for hand-held consumer electronics products such as mobile phones and PDAs with continuing customer demands for “smaller-lighter-more features and lower-cost” has driven reduction of component dimensions and resulting unit mass by orders of magnitude. Typical IC wafer die products in the early 1990's averaged 2 to 5 millimeters per side with thickness dimension of 0.5 to 0.6 millimeters. One decade later, the typical dimensions of functionally equivalent bare die have shrunk to 150 to 250 microns (6 to 10 mils) per side, (cut size) with 50 to 75 micron thickness dimensions. Even full-featured microprocessor die measuring 20 millimeters or more per side are becoming less than paper thin, by means of wafer back grinding, to enable requisite thermal control when in use. Unintended consequences of the foregoing “Sea Changes” in both size and resulting mass of electronic components in general and bare die products in particular include greater fragility of these devices which require further safeguards against damage during handling. In addition, the combination of micron-size footprints and thickness dimensions reduces the mass of each device to the extent that some of the smallest devices can literally defy Newton's Laws of Gravity, and in fact, frequently do so at automated component handling sites. Such particles constitute debris and airborne contamination within clean rooms where such automated component handling takes place and can cause serious injury to machine operators together with irreparable damage to adjacent work in process and processing machinery.
Limitations of present day commercially available carrier tapes to provide needed solutions for problems encountered during automated handling of extremely small low mass electronic components include all of the following:
Limitations of both embossed and punched carrier tapes with cover tapes sealed to retain components within individual cavities.
1. Peel back removal of carrier tape to open each cavity for component retrieval causes very small components to become disoriented within or be ejected from cavities, caused by forces induced by electrostatic discharge together with vibration of carrier tape due to uneven peel-back release of carrier tape from the carrier tape.2. Inability to reduce cavity size to closely match dimensions of tiny components within to maintain component orientation, yet enable components to be removed by conventional pick tools.3. Tendency of very thin devices to migrate to adjacent cavities during reeling and de-reeling of carrier tape. Many of those very thin devices will slide beneath the cover tape, which is not cross-sealed between cavities. This phenomenon is known as “Shingling”Adhesive Backed Carrier Tapes
Pressure sensitive adhesive tape affixed as single or multiple strips to the backside of the component carrier tape must provide an optimum tape-to-component bond, which is minimally sufficient to hold devices securely during automated handling. Excessive adhesion (more than the minimum requirement) will impede rapid, unassisted separation of very small components, especially bare die products, from the adhesive tape backing, using commercially available pick tools for component retrieval and assembly placement.
The choices for adhesive backing tape acceptable for use with carrier tape to contain IC wafer die are limited to those which have been qualified and certified for use in processing IC wafers, and the bare die products singulated therefrom. This restriction is consistent with strict controls of all materials which come into contact with bare IC wafers and wafer die to avoid any measurable amount of contamination which could degrade or cause damage to fragile IC wafer die products. The commercially available pressure sensitive tapes which are qualified and certified for use with bare die vary in adhesive strength ratings. The selection of a minimum adhesive strength is governed by the over arching first requirement for adhesion strength which is sufficient to firmly secure the adhesive tape backing to the base carrier tape material to avoid subsequent de-lamination during reeling and de-reeling.
In point of fact, the minimum adhesion strength of backing tape which is sufficient to ensure its firm attached to the base carrier tape is substantially greater than the minimum adhesive bond strength required for retention of small IC wafer die in fixed repeatable position throughout the entire length of adhesive backed carrier tapes. Accordingly, bare die picked from wafers which have been diced on a solid matrix of qualified wafer dicing tape are individually picked from the dicing tape, assisted by one or more poke-up needles which penetrate the wafer dicing tape backing and rise in unison with the vacuum pick tool to enable separation from the aggressive adhesive dicing tape base.
Adhesive-backed carrier tape offers many advantages for handling these small light weight components and overcomes the major objections voiced by assembly users to conventional pocket tape and punched carrier tape with cover tape(s) for packing and handling extremely small low mass components. However, a major assembly user objection to present forms of adhesive backed carrier tape is the need for a lift pin in each tape feeder to assist the vacuum pick tool in removing each component from the adhesive backing. Such feeders with a lift pin are very costly when compared to feeders for conventional punched carrier tape or embossed pocket tape. In additional these feeders must be custom fitted to each Pick and Place machine platform and integrated with the host computer in order to function successfully. Cost and very limited availability of these special feeders has restricted acceptance of adhesive backed carrier tape to a limited number of high volume production applications.
There are major needs for improved adhesive backed carrier tapes which eliminate the need for a pushup pin or lift pins to assist in removing the component from adhesive backed carrier tape compartments and enable unaided pickup by conventional pick tools used on an automated pick and place assembly machines. There is a further need to provide a choice of predefined consistent low tack levels of adhesion in each compartment to optimize the component-to-tape bonding strength for a wide range of device types and sizes to ensure consistent repeatable capture and take away possession and placement of each device by conventional pick tools without damage to the devices.